iPhone 6 Private Message Difficulties

Hi there I wonder if anyone else has been unable to write a private message to a member using the iPhone 6 ?
I can read messages sent to me but cannot reply because the reply or write message box is off my phone screen !?!
Is there anything I can do to get around this ? Or is the site just not mobile friendly ?
It's very rare I get to use a laptop or pc so really only have my phone screen